Avery and Singer: Unstoppable hot air

November 20th, 2006 by david

Last week I attended a talk by Dennis Avery, author with Fred Singer of Unstoppable Global Warming Every 1500 Years (there is a summary here). The talk (and tasty lunch) was sponsored by the Heartland Institute, and was apparently enthusiastically received by its audience. Still whoozy from a bit of contention during the question period, a perplexed member of the audience told me privately that he thought a Point/CounterPoint discussion might be useful (he didn’t know I wrote for realclimate; it was just a hypothetical thought). But here’s my attempt to accommodate.

Note: The Points are paraphrases from the slides and my notes from Avery’s talk.

Point. The existence of the medieval warm and the Little Ice Age climate intervals, and the 1500 year D-O cycles in glacial climate, proves that the warming in the past decades is a natural phenomenon, not caused by human industry at all.

CounterPoint. The existence of climate changes in the past is not news to the climate change scientific community; there is a whole chapter about it in the upcoming IPCC Scientific Assessment. Nor do past, natural variations in climate negate the global warming forecast. Most past climate changes, like the glacial interglacial cycle, can be explained based on changes in solar heating and greenhouse gases, but the warming in the last few decades cannot be explained without the impact of human-released greenhouse gases. Avery was very careful to crop his temperature plots at 1985, rather than show the data to 2005.

Point. Hundreds of researchers have published on the Little Ice Age and Medieval warm climates, proving that there is no scientific consensus on global warming.

CounterPoint. Natural and human-induced climate changes both exist. Studying one does not imply disbelief in the other.

Point. Human populations of Europe and India thrived during the medieval warm time, so clearly warming is good for us.

CounterPoint. No one asserts that the present-day warmth is a calamity, although perhaps some residents of Tuvalu or New Orleans might feel differently, and the Mayans may have been less than enthusiastic about the medieval climate. The projected temperature for 2100 under business-as-usual is another matter entirely, warmer than the Earth has been in millions of years.

Point. NASA identified a huge energy hole over the tropical Pacific, which sucked out as much heat as doubling CO2. NASA scientists asked modelers to replicate this, and they failed, by 200-400%, even when they knew the answer in advance!

CounterPoint. This appears to be a reference to Chen et al., 2002. Satellite data from the equatorial Pacific showed an increase in IR heat flux to space of about 5 W/m2 from 1985 to 2005, and a decrease in reflected visible light of about 2 W/m2, leaving a 3 W/m2 change in net heat flux.

Avery’s implicit promise would seem to be that with rising CO2, the heavens will part and let the excess energy out, a Lindzenesque mechanism to nullify global warming. The measured change in heat fluxes in the equatorial Pacific is indeed comparable to the radiative effect of doubling CO2 but the CO2 number is a global average, while the equatorial Pacific is just one region. The measurements probably reflect a regional rearrangement of cloud cover or ocean temperature, a decadal variation with no clear implication at all for the global mean heat budget of the Earth. The global heat imbalance has been inferred (Hansen et al, Science, 2005), and it is consistent with rising greenhouse gas concentrations and transient heating of the ocean.

A word about models in science (as opposed to in think-tank economics, Mr. Avery’s home turf). Models would have little use if they were so easy to bend into any answer we thought we knew about in advance. One can always be critical of models, but there is no model that avoids global warming by parting the heavens, or that is exquisitely sensitive to solar variability but insensitive to CO2, the worlds that Mr. Avery wishes for.